This is a very important question to answer.
The truth is, you do not need a telescope to enjoy looking at the
sky. You will never see anything as pretty through a telescope
as you will looking at the sky with your naked eye. Even using
binoculars is more fun. That is because the more powerful the
object you use, the smaller the field of view gets. With
very powerful telescopes you only get to look at a very small part of
the sky.

I have decided I want to buy a telescope:

If you have set your mind on buying a telescope, let
me give you some advice. First of all, before you even open the
box to your new telescope, make sure you have already learned the
constellations. Otherwise you will not be able to find anything
in the sky. You will get frustrated and probably put your new
telescope back in its box.

Numbers:

There are a few numbers you need to find on the
telescope which will help you decide whether or not you want to
purchase it. The first number is the Focal Length. That
is the distance from the mirror, or objective lens, to the lens in
your eyepiece.

If the telescope has a high Focal Length it is
going to be more powerful, but it will give you dimmer views of
whatever you are looking at. If the telescope has a low focal
length your telescope will be less powerful, but have brighter
views. I can't tell you what a good focal length is because
that depends on the size of the mirror, or object lens, and what you
want to use the telescope for.

The next number, though, will help you determine
whether or not the focal length is what you are looking for.
This number is called the Focal Ratio. A high focal ratio means
your focal length is also high. It will look like this on the
telescope: F/6, or F/4, or F/(any number). F/8 is high, or
what we call slow. If you are only after magnification power, this is
the best telescope for you. F/4 is low, or what we call fast. If
you want bright images such as for taking pictures, then you want a fast focal ratio.

The last number you need to be aware of, and by far
the most important, is the diameter of the mirror, or objective
lens. The bigger the diameter the more light your telescope
will be able to gather. This will allow you to see faint objects because the larger mirror will gather more light.

A four inch mirror, which is what many people start
out with, is a good beginner size, mainly because it is the
cheapest. With a four inch mirror you will be able to see many
neat objects, including the rings of Saturn and the clouds of
Jupiter. My telescope has a ten inch mirror.

Power:

Notice that I did not include power as a number you
need to watch for when buying a telescope. That is because
power is not important. The truth is, any telescope can have any power.

When you buy your telescope it will probably
include two or three eyepieces. Each eyepiece will have a
number written somewhere on it. This is the focal length of the
eyepiece. To find the power that your telescope will have with
an eyepiece, divide the focal length of the telescope by the focal
length of your eyepiece.

If my telescope's focal length is 910 mm and my
eyepiece has a focal length of 25 mm, then the power of my telescope
with that eyepiece is 910 divided by 25, which is 36. So the
power of my telescope is 36, or in other words, objects will be
magnified 36 times.

You can also buy a special lens called a Barlow
lens. This lens will double or even triple the power of your telescope.

If my telescope has a focal length of 910 mm and
the eyepiece has a focal length of 4 mm, then my telescope's power will
be 910 divided by 4. This gives a power of 227. Objects
will be magnified 227 times. If I have a Barlow lens, I can
increase that to 445 or even 682. However, if your mirror is not
large enough, objects at that distance will be too dim for you to see
them. All you will see is darkness.